Field of the Invention
The present invention relates to a lens driving mechanism in a lens apparatus, and particularly to a lens apparatus, as well as an image pickup apparatus having the lens apparatus, which varies its focal length or image location by driving multiple optical elements relative to one another.
Description of the Related Art
A conventionally-known lens apparatus includes a cam mechanism and optical elements such as a lens support frame that supports lenses and an aperture device that adjusts the amount of light, and performs zooming, focusing, and light amount adjustment by using the cam mechanism to move the optical elements relative to one another in a direction of an optical axis. In a typical cam mechanism, cam grooves are formed on an inner circumferential surface of a moving barrel, and cam pins are attached to the ions support frame to engage with the cam grooves. Rotating the moving barrel moves the lens support frame inside the moving barrel forward and backward along the cam grooves. Since there is a play between each cam groove and its corresponding cam pin, the tilting (direction and angle) of the lens support frame varies depending on the direction in which the moving barrel is rotated. There is therefore an increasing demand especially for a lens apparatus required to have high definition in peripheral resolution to include a structure for biasing the lens support frame in a certain one of its moving directions to retain the tilting of the lens support frame even when the moving barrel is rotated in the opposite direction (referred to as reverse rotation below). The following structure has been disclosed as a structure for retaining the tilting of the lens support frame even in the reverse rotation.
In a lens tilt reduction structure disclosed in Japanese Patent Application Publication No. H11-326734, multiple spring members are provided between two zoom lens units to apply biasing forces evenly to the cam pins of each zoom lens unit. Backlash between the cam grooves and the cam pins is thereby reduced.
In a case of a lens support frame for a heavy lens, the spring members need to apply large biasing forces to retain the tilt direction of the lens support frame in the reverse rotation. Such increased biasing forces, however, increase the kinetic frictions generated between the cam grooves and the cam pins sliding therein. In other words, a large torque is necessary to turn an operation ring provided around a lens barrel to move the moving barrel in the optical axis direction.